sequence function: find-steps-between

    description:
        find-steps-between(ket, ket)
        find the steps between the given kets
        currently potentially quite slow!

    examples:
        load early-us-presidents.sw
        find-inverse[president-number, president-era, full-name]

        find-steps-between(|person: George Washington>, |number: 6>)
            |person: George Washington> . |Washington> . |year: 1797> . |Adams> . |year: 1801> . |Jefferson> . |party: Democratic-Republican> . |year: 1825> . |Q Adams> . |number: 6>

    future:
        optimize it with Dijkstra's algorithm
        (since current algorithm is horrible!)
        make it work with path-ways between sequences too.
        
    see also:
        find-path-between